Response to EGFR blockade

ABSTRACT

Recent large-scale analyses have demonstrated that the genomic landscape of human cancer is complex and variable among individuals of the same tumor type. Such underlying genetic differences may in part be responsible for the varying therapeutic responses observed in cancer patients. To examine the effect of somatic genetic changes in colorectal cancer on sensitivity to a common targeted therapy, we performed complete exome sequence and copy number analyses of 129 tumors that were KRAS wild-type and analyzed their response to anti-EGFR antibody blockade in patient-derived tumorgraft models. In addition to previously identified genes, we detected mutations in ERBB2, EGFR, FGFR1, PDGFRA, and MAP2K1 as potential mechanisms of primary resistance to this therapy. Alterations in the ectodomain of EGFR were identified in patients with acquired resistance to EGFR blockade. Amplifications and sequence changes in the tyrosine kinase receptor adaptor gene IRS2 were identified in tumors with increased sensitivity to anti-EGFR therapy. Therapeutic resistance to EGFR blockade could be overcome in tumorgraft models through combinatorial therapies targeting actionable genes. These analyses provide a systematic approach to evaluate response to targeted therapies in human cancer, highlight additional mechanisms of responsiveness to anti-EGFR therapies, and provide additional avenues for intervention in the management of colorectal cancer.

This application is a National Stage application under 35 U.S.C. § 371of International Application No. PCT/US2016/012268 having anInternational Filing Date of Jan. 6, 2016, which claims benefit ofpriority from U.S. Provisional Application Serial No. 62/100,110, filedon Jan. 6, 2015.

This invention was made with government support under grant CA121113awarded by the National Institutes of Health. The government has certainrights in the invention.

TECHNICAL FIELD OF THE INVENTION

This invention is related to the area of cancer therapy. In particular,it relates to primary and acquired resistance to cancer therapy agents,as well as determinants of increased sensitivity.

BACKGROUND OF THE INVENTION

Colorectal cancer (CRC) is the third most common cancer world-wide with1.2 million patients diagnosed yearly, and over 600,000 dying of thedisease. In CRCs, tumor progression is accompanied by a series ofgenetic changes that affect several oncogenes and tumor suppressor genesand their cellular pathways. These include dysregulation of the APC/WNTpathway (1-3), mutations of KRAS or BRAF oncogenes in early stagedisease (4-6), activation of the PI3K pathway through alterations inPIK3CA or PTEN (7, 8), and alterations in the p53 and TGF beta pathwaysin later stages of disease progression (9-14). Additional geneticabnormalities have been observed in key signaling genes (15-17) andthrough large scale genomic analyses of CRCs (18-20).

In late stage CRC, the most commonly used targeted therapies aremonoclonal antibodies cetuximab and panitumumab which inactivate EGFR(21). Recent studies of CRC resistance to anti-EGFR antibody therapyhave identified alterations in KRAS (22-24), NRAS (25), BRAF (25-27),PIK3CA (25, 28), along with amplification of MET (29) and ERBB2 (30, 31)as likely mechanisms of primary resistance to this therapy. Alterationsin many of these genes as well as mutations in EGFR have been shown toprovide acquired (secondary) resistance to EGFR inhibition (29, 32-34).

Despite these efforts, additional mechanisms of resistance to EGFRblockade are thought to be present in CRC (35) and little is known aboutdeterminants of sensitivity to this therapy. There is a continuing needin the art for a systematic genome-wide study in CRC to identify geneticchanges associated with responsiveness to any targeted therapy.

SUMMARY OF THE INVENTION

According to one aspect of the invention a method is provided fortreating a tumor in a human. A sample from the tumor is tested andamplification or an activating mutation in tyrosine kinase receptoradaptor gene IRS2 is determined. The human is treated with or prescribedan inhibitor of a receptor selected from the group consisting of: MET,ERBB2, EGFR, FGFR, and PDGFR.

According to another aspect of the invention a method is provided fortreating a tumor resistant to EGFR blockade in a human. An inhibitor ofFGFR1 and an inhibitor of EGFR are administered to the human.

According to yet another aspect of the invention another method oftreating a tumor in a human is provided. The tumor is resistant to EGFRblockade. An EGFR kinase inhibitor and an anti-EGFR antibody areadministered to the human.

According to still another aspect of the invention an additional methodis provided for treating a tumor resistant to EGFR blockade in a human.An inhibitor of MEK1 and an inhibitor of ERK are administered to thehuman.

According to another aspect of the invention a method is provided fortreating a tumor in a human. The tumor is resistant to EGFR blockade. Amonoclonal antibody to EGFR that binds to an epitope distinct from theepitopes bound by cetuximab and panitimumab is administered to thehuman.

According to yet one more aspect of the invention a method is providedfor treating a human with a tumor. A sample from the tumor is tested anda mutation in a gene selected from the group consisting of: FGFR,PDGFRα, MAP2K1, and ERBB2 is determined. The human is then treated withan antibody to EGFR.

According to an additional aspect of the invention a method is providedfor treating a human with a tumor. The tumor is treated with a firstantibody to EGFR. Then a sample from the tumor is tested and a mutationin EGFR's ectodomain is determined. The treatment is then modified toinclude an EGFR kinase inhibitor or an anti-EGFR antibody to a distinctepitope from the epitope bound by the first antibody.

These and other embodiments which will be apparent to those of skill inthe art upon reading the specification provide the art with methods toovercome primary and secondary resistance in tumors to EGFR blockade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic diagram of integrated genomic and therapeuticanalyses. Resected colorectal cancer hepatic metastases were directlyimplanted in NOD/SCID mice. One hundred thirty seven early passagetumorgrafts and matched normal samples were analyzed using whole exomesequence and copy number analyses. In parallel, tumorgrafts wereestablished and evaluated for response to cetuximab in preclinicaltherapeutic trials. For a subset of cases, pre-implanted material andcetuximab treated hepatic metastases were also analyzed by targetedsequencing. Integration of genomic and therapeutic information was usedto identify candidate resistance and response genes, as well as todesign preclinical trials using therapeutic compounds to overcomeresistance to anti-EGFR blockade.

FIG. 2. Effect of cetuximab treatment on growth of colorectal tumorswith different somatic alterations. The change in tumor growth inpreclinical trials is determined as the fold growth or shrinkage frombaseline in 116 KRAS wild-type tumorgrafts. Candidate alterationsrelated to therapeutic resistance or sensitivity are shown in theindicated colors (complete list of alterations are in Tables S3, S4 andS6). For the following genes a subset of alterations are indicated: METamplification; FGFR1 amplification; PDGFRA kinase domain mutations; BRAFV600 hotspot mutations; PTEN homozygous deletion or truncatingmutations; PIK3CA exon 20 mutations; EGFR ecto- and kinase domainmutations and amplifications. Tumor growth values are thresholded at200%.

FIG. 3. EGFR signaling pathway genes involved in cetuximab resistance orsensitivity. Altered cell surface receptors or members of RAS or PI3Kpathways identified in this study are indicated. Somatic alterationsrelated to resistance or sensitivity are highlighted in red or greenboxes, respectively. The percentages indicate the fraction of KRAS WTtumors containing the somatic alterations in the specified genes. Forthe following genes a subset of alterations are indicated: PDGFRA kinasedomain mutations; EGFR ecto- and kinase domain mutations andamplifications.

FIG. 4A-4C. Genetic alterations involved in secondary resistance to antiEGFR therapy. FIG. 4A. The location of the secondary resistancemutations detected in EGFR are analyzed through structural models of thesoluble extracellular region of EGFR (domains I-IV) and the antigenbinding fragment (Fab) of cetuximab. The G465 residue altered in CRC104and CRC177 are shown in red while the S492 residue that has beendescribed to confer cetuximab resistance (32) is shown in yellow. FIG.4B. Schematic of evolution of EGFR secondary resistance in the twoanalyzed CRCs with acquired resistance. Cetuximab-naïve samples weresequenced to investigate whether somatic mutations affecting EGFR aminoacid 465 (indicated by red circles) were detectable prior to treatment.The fraction of mutant tags detected for each sample is indicated. FIG.4C. Analysis of the fraction of TP53 mutant reads (vertical axis)compared to the fraction of reads with EGFR ectodomain mutations(horizontal axis) show the level of EGFR alterations in differentlesions when controlled for tumor cellularity.

FIG. 5A-5D. Therapeutic intervention in preclinical trials to overcomeresistance to anti-EGFR antibody blockade. Tumor growth curves intumorgraft cohorts (n=6 for each treatment arm) derived from individualpatients with (FIG. 5A) FGFR1 amplification (CRC477), (FIG. 5B) EGFRkinase mutation (CRC334), (FIG. 5C) MAP2K1 K57N mutation (CRC343), and(FIG. 5D) EGFR ectodomain mutations (CRC104 left and CRC177 right)treated with placebo or targeted treatments.

FIG. 6A-6D. (Supplementary Table 5) Frequently Altered Genes in KRAS WTmetastatic CRC

FIG. 7A-7CCCC. (Supplementary Table 6) Integration of SomaticAlterations with Response to anti-EGFR Blockade

DETAILED DESCRIPTION OF THE INVENTION

The inventors have developed methods for treating tumors that havedeveloped resistance to agents which blockade or inhibit epidermalgrowth factor receptor (EGFR). The inventors have also found the certaincombinations of anti-tumor agents act synergistically to inhibit tumorprogression. The inventors have also found that certain genetic changesindicate sensitivity to EGFR blockade or inhibition.

Agents which can be used to inhibit or block EGFR include any that areknown in the art. The agents may be, for example, small moleculeinhibitors, particularly kinase inhibitors, or antibodies. Theseinclude, without limitation, Afatinib, Bevacizumab, BMS-690514,Brivanib, Cabozantinib, Cetuximab, Cixutumumab, Dacomitinib,Dalotuzumab, Figitumumab, Ganitumab, Neratinib, Onartuzumab,Rilotumumab, Sorafenib, Sunitinib, Tivantinib, and Vandetanib.

Tumors which can be treated according to the invention include any whichare treated with EGFR inhibitors or blocking agents. Such tumors includewithout limitation non-small-cell lung cancer, pancreatic cancer, breastcancer, colon cancer, rectal cancer, and glioma. Other tumors which maybe treated include prostate cancer, ovarian cancer, cervical cancer,uterine cancer, melanoma, astrocytoma.

Testing for amplification or activating mutations in tyrosine kinasereceptor adaptor gene IRS2 can be accomplished by any means known in theart. Targeted assays for this particular gene or assays of the entiregenome may be used. Targeted assays may use amplification andsequencing, amplification and specific probes, digital amplification,primer specific extension, etc. Assays of the whole genome or wholeexome may be used. Any format and technique may be selected as isconvenient.

Testing for BRAF mutations or MET amplification or FGFR1 amplificationor FGFR mutations, PDGFR mutations, MAP2K1 mutations, and ERBB2mutations can be accomplished by any techniques known in the art. Genesequencing, mutation specific probes, mutation-specific amplification,digital amplification or digital karyotyping, are examples of techniqueswhich may be used to identify mutations or amplifications.

Inhibitors of MET, ERBB2, FGFR, and PDGFR which can be administered orprescribed are any which are known in the art. They may be, for example,antibodies or small molecule kinase inhibitors. These include withoutlimitation: nilotinib, AM7, SU11274, BMS-777607 and PF-02341066,MK-2461, JNJ-38877605, PF-04217903, GSK 1363089 (XL880, foretinib),trastuzumab, AZD4547, Ponatinib, Dovitinib, BGJ398, E-3810,JNJ-42756493, ARQ 087, Tyrphostin AG 1295, Pan-HER, and AG-370.

Mutations which may be identified in EGFR related to resistance tocertain anti-EGFR antibodies are V843I, G465E, and G465R These mutationsmay be associated with resistance to cetuximab or panitimumab.

MEK inhibitors which may be used therapeutically without limitationinclude ACZD6244, Trametinib (GSK1120212), Selumetinib, Binimetinib orMEK162, PD-325901, Cobimetinib or XL518, CI-1040, and PD035901. ERKinhibitors which may be used include SCH772984.

The studies described below represent the most comprehensive analysis ofgenetic determinants of response to a targeted therapeutic agent incancer. Through this effort we detected essentially all previously knownmechanisms of primary resistance to cetuximab in CRC. Our dataidentified additional candidate mechanisms of primary and secondaryresistance through alterations affecting EGFR, its downstream signalingpathway, and other cell surface receptors (FIG. 3). These alterations,together with KRAS, account for over three quarters of cetuximabresistant tumors and suggest that the vast majority of underlying causesof primary resistance have now been determined and can be identifiedprior to the initiation of anti-EGFR treatment.

The fact that a majority of tumors contain genetic changes resulting inresistance to EGFR therapy is a clinical challenge for late stage CRCpatients. Fortunately, some of the mechanisms of resistance provideavenues for intervention, including amplification of FGFR1, mutation ofPDGFR1 or ERBB2, and the previously identified amplification of ERBB2and MET receptors. These receptors are targets of therapies that arealready established or in development and could be useful in tumors withmutations in these genes. The observed alterations in MAP2K1 alsosuggest that targeting pathways downstream of EGFR, including the MAPKpathway, may prove beneficial (57). As we have shown through ourtumorgraft studies, a combination of therapies targeting both theprotein products encoded by resistance genes as well as EGFR or othersignaling partners are likely to be crucial for inhibiting the multiplegenetic components within a tumor. The high fraction of tumors withactionable alterations suggests that additional combinatorial therapiesmay be useful for CRC patients.

An unexpected finding of this study was the identification of anadditional mechanism of sensitivity to anti-EGFR therapy. Although manylate stage patients with KRAS wild-type tumors receive cetuximab orpanitumumab, less than 15% have durable responses (24, 58). We haveshown that in addition to the absence of other potential resistancealterations, the presence of genetic changes in IRS2 was significantlyassociated with response to cetuximab therapy. IRS2 signaling isactivated through ligand-mediated cell surface receptors, including EGFR(59, 60). Our data suggest that IRS2 alterations may identify tumorsthat are most dependent on receptor signaling and therefore mostsensitive to its therapeutic inhibition. Consistent with this predictionare reports that IRS2 amplification is a significant indicator ofresponse to the IGF1R inhibitor figitumumab in colorectal and lungcancer cell lines (61). Given the interaction of IRS2 with multiple cellsurface receptors, we predict that combinatorial inhibition of thereceptors in tumors with IRS2 alterations may provide even morelong-lasting responses in such patients.

This study highlights information that may be obtained through theintegration of large-scale genomic and targeted therapeutic analyses inCRC. Although careful measures were taken to increase the sensitivity ofdetecting genetic changes in these tumors, some alterations may not havebeen detected due to low tumor purity, poor sequence mapping, or lowcoverage using next-generation sequencing approaches. Likewise, althoughthe use of tumorgrafts has shown promise as “avatars” for individualpatient therapies (62), they may not fully represent the range oftherapeutic responses observed clinically. Despite these limitations,these data provide an unprecedented view into mechanisms of response toEGFR blockade. Through integrated genomic analyses, we have identified acompendium of markers of primary and secondary resistance as well assensitivity in this disease. This information provides a framework foranalysis of responses to targeted therapies in CRC and suggestsinterventional clinical therapies using combinatorial therapies based onpotentially actionable alterations.

The above disclosure generally describes the present invention. Allreferences disclosed herein are expressly incorporated by reference. Amore complete understanding can be obtained by reference to thefollowing specific examples which are provided herein for purposes ofillustration only, and are not intended to limit the scope of theinvention.

Example 1

Overall Approach

As KRAS alterations are a well-established mechanism of resistance toEGFR inhibitors (22-24), we selected 137 colorectal tumors that werewild-type at codons 12, 13 and 61 of KRAS as determined by Sangersequencing (36). The colorectal cancers analyzed were all livermetastases in patients who underwent potentially curative resections. Toelucidate genetic alterations in the coding regions of these cancers, weused next-generation sequencing platforms to examine the entire exomesof matched tumor and normal specimens (36) (FIG. 1. Given the lowneoplastic cellularity of colorectal cancers (37), we enriched forneoplastic cells using patient-derived tumorgrafts and performed deepsequencing (high coverage) of the enriched tumor samples and matchednormal DNA (36). This approach allowed us to identify sequence changes,including single base and small insertion or deletion mutations, as wellas copy number alterations in >20,000 genes in the whole-exome analyses.We obtained a total of 4.23 Tb of sequence data, resulting in an averagecoverage within the target regions of nearly 150-fold for each patient.

Sequence analyses of 135 of 137 tumors identified a median of 117somatic mutations in each cancer, similar to previous whole exomestudies in CRC (18-20). Two tumors displayed an elevated number ofsomatic sequence alterations (2979 and 2480 changes per exome),consistent with a mutator phenotype (20). Common CRC driver genes,including APC, TP53, PIK3CA, PTEN, SMAD4, FBXW7, TCF7L2 and SOX9 wereidentified at expected frequencies in the tumors analyzed (FIG. 6; TableS5). A total of 8 tumors were identified as having KRAS alterations atcodons 12 or 13 that were not initially detected by Sanger sequencingand were excluded from further analysis.

Example 2

Primary Resistance to Anti-EGFR Therapy

To evaluate whether the alterations that we identified were associatedwith resistance to EGFR inhibitors, we determined tumorgraft response tocetuximab therapy for 116 of the CRCs after tumor implantation (FIGS. 1,2). The volume of each tumorgraft was evaluated at three and six weeksin 12 or 24 mice (depending on individual models) that were randomizedto treatment and control arms at a 1:1 ratio. Tumors were categorized asshowing disease progression (36 cases, 31%), regression (39 cases, 34%),or stabilization (41 cases, 35%) (36). We compared the integratedprofiles of genomic alterations and therapeutic responses of the tumorsanalyzed and focused on genes that were predominantly altered in casesshowing tumor growth in the presence of anti-EGFR therapy (FIG. 2, FIG.7A-7CCCC; Table S6). Among tumorgrafts with disease progression orstabilization, we detected coding alterations in all genes known to beinvolved in EGFR therapeutic resistance: NRAS sequence mutations incodons 12 or 61 (7 cases), BRAF V600E mutation (3 cases), METamplification (3 cases), and ERBB2 amplification (4 of 5 cases).Additionally, 3 of 4 tumors with alterations in exon 20 of PIK3CA and 4of 5 tumors with protein truncating or homozygous deletions of PTEN wereresistant to anti-EGFR blockade, consistent with previous studies (25,38).

In addition to genes known to confer resistance to EGFR blockade, wealso evaluated potential mechanisms of resistance that have not beenpreviously described in colorectal cancer. We focused on other cellsurface protein kinase receptors or members of the EGFR signalingpathway and identified candidate genes that were preferentially alteredin therapy-resistant tumors (FIGS. 2, 3; Tables S3, S4) We observedpoint mutations affecting the ERBB2 kinase domain, including in twopatient tumors with exactly the same change at 777V>L and another tumorharboring an 866L>M mutation, as well as a sequence change in theectodomain at 310S>Y, all of which correlated with cetuximab resistance.Although ERBB2 amplification has been liked to colorectal cancer (30,31, 37), sequence alterations are more frequently observed in othertumor types including breast and lung cancers (39, 40) and have not beenlinked to therapeutic resistance of anti-EGFR blockade. Previous reportshave shown that alterations at residue 777 lead to constitutiveactivation of ERBB2 both in vitro and in vivo (40). These data suggestthat somatic mutations in ERBB2 may provide an alternative mechanism forERBB2 pathway activation that is complementary to ERBB2 amplification incolorectal cancer. Similar to ERBB2, we found sequence alteration in thekinase domain of EGFR (843V>I) in one case that showed tumor growth inthe presence of cetuximab. Although EGFR kinase alterations are rare incolorectal cancer (41, 42), the observed case suggests that in principlesuch changes may provide a mechanism of resistance to anti-EGFR therapy.

We identified alterations in additional cell surface protein kinasereceptors: amplification of the fibroblast growth factor receptor FGFR1and sequence alterations in the platelet-derived growth factor receptorPDGFRA. Each of these was altered in four of the 129 CRC samplesanalyzed (8 samples total, 6%). Tumor growth was observed in allcetuximab treated cases with FGFR1 and PDGFRA alterations. FGFR1 is aknown driver gene in a variety of human cancers (43) and has beenreported to be amplified in different tumor types, including lungcancer, breast and colorectal cancers (44-46). PDGFRA is a tyrosinekinase receptor that is known to be mutated in gastro-intestinal stromaltumors (47). The detected sequence alterations in PDGFRA, including amutation that affected the same residue in two different patients(981R>H), were all located in or near the protein catalytic domain ofthe protein. Similar to ERBB2 and MET, the receptors encoded by thesegenes transmit signals through the RAS/MEK cascade and when mutated canlead to constitutive activation of oncogenic pathways (43, 48).

We further examined candidate alterations within the RAS pathway andobserved a nucleotide sequence change resulting in an amino acid swap oflysine to arginine at residue 57 in the mitogen activated protein kinasekinase gene MAP2K1 in a cetuximab-resistant case. Alterations of MAP2K1at the same or nearby residues have been described in CRC, melanoma andlung cancer (49, 50) and are adjacent to the catalytic domain. The 57K>Nalteration has been shown to confer IL-3-independent cell growth in BaF3cells, suggesting that this mutation may be functionally active (49).Overall, the enrichment of mutations in known and previously unknownpathways in the resistant tumorgrafts was statistically significant(p<0.001, Welch Two Sample t-test) and suggests that alterations in anyof these members may be sufficient to render cells insensitive to EGFRinhibition (36).

Example 3

Acquired Resistance to Anti-EGFR Therapy

Although some tumors initially respond to cetuximab, virtually all CRCpatients treated with anti-EGFR therapy eventually develop diseaserecurrence (38). In our analyses, 22 tumors were resected from patientsthat had received cetuximab within six months prior to surgicalresection. We examined whether novel alterations in these cases may havearisen as acquired (secondary) resistance to this therapy. Two of these22 tumors (9%) had G to A sequence substitution in the EGFR codingregion at nucleotide positions 1393 and 1394, resulting in asubstitution of glycine to glutamic acid (465G>E) or arginine (465G>R)in domain III of the extracellular portion of the receptor. Sequencingof normal liver from these patients revealed only wild-type sequences atthese residues and confirmed that the 465G>E and 465G>R mutations weresomatic. Structural analyses suggested that these mutations were likelyto affect cetuximab binding as they were located at the interface ofEGFR—cetuximab interaction (FIG. 4A). Interestingly, through anintervening parallel beta-sheet, G465 is structurally adjacent toresidue S492 within the ectodomain region of EGFR that has been shown,when altered, to interfere with cetuximab binding (32) (FIG. 4A).

To determine whether the putative resistance mutations affecting EGFRamino acid residue 465 were present in the cetuximab naïve tumor or wereacquired following treatment, we examined pre- and post-therapyspecimens for subjects CRC104 and CRC177 whose tumor harbored the 465G>Eand 465G>R EGFR ectodomain mutations, respectively (FIG. 4B). Targetedcapture and deep sequencing (723× coverage) of the post-cetuximabhepatic metastatic specimen resected from patient CRC104 confirmed the465G>E mutation while the original colectomy specimen obtained beforetreatment did not have a detectable alteration (530× coverage) (FIG.4C). Interestingly, patient CRC104 experienced an early relapse inDecember 2009 while on treatment with cetuximab, suggesting resistanceto anti-EGFR therapy in the clinical setting. Similarly, longitudinalanalyses of tumor specimens from subject CRC177 revealed wild-type EGFRin the pre-treatment biopsy of a liver metastasis (December 2009),emergence of the 465G>R mutation in a liver deposit resected aftercetuximab-containing neo-adjuvant therapy (June 2010), and persistenceof this mutation in resected tissue from a second-stage hepatectomyafter an additional line of neo-adjuvant cetuximab (September 2010)(FIG. 4B, 4C). Although these findings do not rule out the presence ofthese alterations in one or a small number of cells in the pre-treatmenttumors, the genomic analyses suggest that the alterations were clonallydetectable only after selection in the presence of cetuximab.

Example 4

Determinants of Sensitivity to EGFR Blockade

Among colorectal cancer patients that have KRAS wild-type tumors, only12-17% have durable responses to anti-EGFR antibody monotherapy (24,27). We wondered whether such responses may be due to alterations ingenes that confer therapeutic sensitivity in addition to the absence ofalterations that confer resistance. Amplification of the EGFR gene hasbeen shown to increase anti-EGFR antibody sensitivity (51, 52) but othergenetic markers of cetuximab response have not yet been identified. Inour analyses, EGFR was found to be amplified in two tumors that showedeither regression (CRC98, 26 fold amplified) or disease stabilization(CRC400, 3 fold amplified) (FIG. 2).

To discover indicators of anti-EGFR response, we examined the mutationallandscape of tumors that showed tumorgraft regression following in vivotreatment with cetuximab. Given the importance of EGFR signaling, weanalyzed other members of the pathway that were preferentially mutatedin responsive tumors (36). The only other gene within the EGFR pathwaythat we identified to be associated with cetuximab response was IRS2, acytoplasmic adaptor that mediates signaling between receptor tyrosinekinases and downstream targets (FIG. 2, FIG. 7A-7CCCC; Table S6)(p<0.05, Welch Two Sample t-test) (36). This gene had amplifications orsequence alterations in 7 CRC tumors (6%) that showed increasedsensitivity or stable disease when treated with cetuximab. Similarly,expression analyses of the CRC tumors identified increased IRS2 levelsas a significant predictor of cetuximab sensitivity (p<0.001, Student'st-test) (36). Two additional tumorgrafts with IRS2 alterations (CRC508and CRC106) that were not responsive to cetuximab harbored a METamplification or BRAF mutation, highlighting that IRS2 mutation islikely to be predictive for anti-EGFR response in cases without othermechanisms of resistance to EGFR therapy. We and others have previouslyidentified alterations in IRS2 in CRCs and other tumor types (17, 20,37, 53), but no reports to date have linked the effects of thesealterations to therapeutic sensitivity.

Example 5

Therapeutic Targets for CRC Patients

Given the poor outcome of patients diagnosed with late stage colorectalcancer, and especially of those that are resistant to anti-EGFRinhibitors, we investigated whether mutant genes observed in individualcases may be clinically actionable using existing or investigationaltherapies. We examined altered genes that were associated with 1)FDA-approved therapies for oncologic indications, 2) therapies inpublished prospective or retrospective clinical studies, and 3) ongoingclinical trials for patients with colorectal cancer or other tumortypes.

Through these analyses we identified somatic alterations withpotentially actionable consequences in 100 of the 129 patients (77%). Totest whether any of the identified actionable alterations may besuccessfully targeted in tumors with cetuximab resistance, we used thetumorgrafts to perform proof of principle trials for specific targetedtherapies. We first chose as an example a cetuximab-resistant tumor withFGFR1 amplification (CRC477) and examined whether inhibition of bothFGFR1 and EGFR would be more effective than inhibition of EGFR alone.The rationale for this approach is that such tumors have multiple activepathways providing growth signals from the cell surface that need to besimultaneously targeted. The original tumor specimen was seriallypassaged in vivo until production of final treatment arms. In vivoadministration of the selective FGFR kinase inhibitor BGJ398, which iscurrently in clinical trials (54), began when the tumorgrafts reached anaverage volume of approximately 400 mm3. Mice were randomized into 4independent treatment cohorts, each consisting of 6 mice: (i) vehicle(placebo); (ii) cetuximab alone; (iii) BGJ398 alone; (iv) cetuximab andBGJ398. We confirmed resistance to cetuximab alone and as may beexpected using a single pathway inhibitor, the tumorgraft was alsoresistant to BGJ398 alone (FIG. 5A). However, a combination of BGJ398together with cetuximab led to a substantial and durable suppression oftumor growth in all treated mice (p<0.01, two-way ANOVA). This modelconfirmed that combinatorial therapies may be effective in overcomingEGFR therapeutic resistance in tumors with alterations in other cellsurface receptors.

A similar approach was used to evaluate the EGFR small-moleculeinhibitor afatinib in tumor CRC334 containing sequence change 843V>I inthe protein kinase domain of EGFR (FIG. 5B). In this case, the mechanismof resistance to cetuximab could be through constitutive activation ofthe receptor kinase domain, abolishing dependence on extracellularsignaling. We wondered whether afatinib could overcome cetuximabresistance as it has been shown to be effective primarily in EGFR mutanttumors. However, the resistant subclone containing the EGFR kinasedomain alteration only affected 23% of the tumor cells in this samplewhich was highly tumor-enriched as measured by the prevalence of geneticalterations in highly mutated genes such as TP53 (present in 98% of theanalyzed tumor). Given this heterogeneity, targeting the tumorgraftswith afatinib or cetuximab alone was not effective. In contrast, acombination of afatinib and cetuximab, presumably targeting bothcomponents of the tumor, resulted in marked and long lasting tumorgrowth inhibition (p<0.01, two-way ANOVA).

We also targeted resistance-conferring alterations in EGFR downstreameffectors. Case CRC343 with MAP2K1 57K>N substitution, encoding a mutantform of MEK1, was treated with small-molecule inhibitors against MEK1(AZD6244) or against its direct substrate ERK (SCH772984). Similar tocetuximab, single-agent blockade of MEK1 was unproductive. However,inactivation of both MEK1 and ERK led to effective arrest of tumorgrowth (FIG. 5C) (p<0.01, two-way ANOVA). These results encourageconcomitant targeting of MEK1 and ERK as a promising strategy toovercome aberrant MEK and potentially RAS signaling in CRC.

Next, we evaluated whether alternative therapeutic approaches may behelpful in tumors with acquired (secondary) cetuximab-resistantalterations in the EGFR ectodomain. As previous reports have shown thatcetuximab-resistant tumors with 492S>R alterations in EGFR are sensitiveto panitumumab (32), we wondered whether tumors with alterations at thestructurally adjacent residue 465 in the ectodomain may also besensitive to this therapy. Tumorgrafts derived from patient CRC104 withEGFR 465G>E mutation were randomized into independent treatment cohorts(n=6 for each arm) consisting of different anti-EGFR therapies orvehicle control. Unlike tumors with alterations at residue 492, thetumorgraft was poorly sensitive to panitumumab. Structural analysesindicate that S492 belongs solely to the cetuximab binding site withinthe large conformational epitopes of cetuximab and panitumumab in EGFRdomain III. Conversely, G465 is located in the center of the region inwhich the epitopes of both antibodies overlap (55), suggesting thatmutations affecting this codon may weaken antigen recognition by boththerapies. This lack of sensitivity was not due to absence of EGFRdependence as kinase inhibition of EGFR using afatinib resulted inmanifest reduction of tumor growth that could be further augmented byconcomitant administration of panitumumab (p<0.01, two-way ANOVA),likely due to residual antibody activity (FIG. 5D).

We also explored whether EGFR inhibition by therapeutic antibodiestargeting epitopes far from G465 could overcome resistance. We usedPan-HER (Symphogen), a monoclonal antibody mixture against several ERBBfamily members with an anti-EGFR component that binds epitopes differentfrom those recognized by cetuximab and panitumumab (56) (FIG. S1).Notably, for this tumor Pan-HER was the most effective in inducing tumorregression (FIG. 5D) (p<0.01, two-way ANOVA), further suggesting thatmutations in G465 do not affect the biological function of the receptorand are permissive for target blockade by antibodies that interact withother regions of the EGFR ectodomain. Similar results using theafatinib-panitumumab combination or Pan-HER were observed in CRC177 withEGFR 465G>R mutation (FIG. 5D).

Example 6

Materials and Methods

Specimen Obtained for Sequencing Analysis

The study population consisted of matched tumor and normal samples from137 colorectal cancer patients that underwent surgical resection ofliver metastases at the Candiolo Cancer Institute (Candiolo, Torino,Italy), the Mauriziano Umberto I Hospital (Torino) and the San GiovanniBattista Hospital (Torino) from 2008-2012. Informed consent for researchuse was obtained from all patients at the enrolling institution prior totissue banking and study approval was obtained from the differentcenters. Tumors with KRAS alterations at codons 12, 13 and 61 that weredetected using Sanger sequencing were not included in the study. Fromthe resected tumor samples, tumorgraft models were established asdescribed below. Following exome sequence analyses, 8 patients weredetected to have KRAS mutations (patients CRC18, CRC58, CRC68, CRC237,CRC312, CRC328, CRC344, CRC382) and were excluded from further analyses.

Tumorgraft Model and In Vivo Treatments

Tissue from hepatic metastasectomy in affected individuals wasfragmented and either frozen or prepared for implantation as describedpreviously (1, 2). NOD/SCID (nonobese diabetic/severe combinedimmunodeficient) female mice (4 to 6 weeks old) were used for tumorimplantation. Nucleic acids were isolated from early passagedtumorgrafts. The remaining tumorgraft material was further passaged andexpanded. Animals (at least 6 mice per cohort) with established tumorsdefined as an average volume of 400 mm3 were treated with vehicle ordrug regimens, either as a single-agent or in combination as indicated:cetuximab (Merck, White House Station, N.J.) 20 mg/kg/twice-weekly i.p.;BGJ398 (Sequoia Research Products, Pangbourne, United Kingdom) 30mg/kg/once-daily by oral gavage; panitumumab (Amgen, Thousand Oaks,Calif.), 20 mg/kg/twice-weekly i.p.; afatinib (Sequoia ResearchProducts), 20 mg/kg/once-daily by oral gavage; AZD6244 (Sequoia ResearchProducts), 25 mg/kg/once-daily by oral gavage; SCH772984 (ChemieTek,Indianapolis, Ind.), 75 mg/kg/once daily i.p.; Pan-HER (Symphogen), 60mg/kg twice-weekly i.p. Each tumorgraft was evaluated at three and sixweeks in 12 or 24 mice (depending on individual models) that wererandomized to treatment and control arms at a 1:1 ratio. For assessmentof tumor response to therapy, we used volume measurements normalized tothe tumorgraft volume at the time of cetuximab treatment initiation.Tumorgrafts were classified as follows: (i) tumor regression with adecrease of at least 35% in tumor volume, (ii) disease progression withat least a 35% increase in tumor volume, and (iii) disease stabilizationwith a tumorgraft volume at levels <35% growth and <35% regression.Tumors displaying regression or stabilization continued treatment foradditional 3 weeks. Tumor size was evaluated once per week by calipermeasurements and the approximate volume of the mass was calculated. Invivo procedures and related biobanking data were managed using theLaboratory Assistant Suite (LAS), a web-based proprietary datamanagement system for automated data tracking (3). All experiments wereconducted with approval from the Animal Care Committee of the CandioloCancer Institute, in accordance with the Italian legislation on animalexperimentation.

Massively Parallel Paired-End Sequencing and Somatic MutationIdentification

Sample library construction, exome or targeted capture, next generationsequencing, and bioinformatic analyses of tumor and normal samples wereperformed as previously described (4). In brief, fragmented genomic DNAfrom patient's tumor, tumorgraft developed from a liver metastasis ornormal samples (adjacent non-cancerous liver or peripheral blood) wasused for whole-exome enrichment or targeted regions using the AgilentSureSelect 50 Mb kit according to the manufacturer's instructions(Agilent, Santa Clara, Calif.). Captured DNA libraries were sequencedwith Illumina HiSeq 2000 Genome Analyzer or a MiSeq System (Illumina,San Diego, Calif.). Sequence reads were analyzed and aligned to thehuman genome sequence (hg18) with the Eland v.2 algorithm in CASAVA 1.7software (Illumina, San Diego, Calif.). Potential somatic mutations andcopy number alterations were identified as described previously (4, 5).Mutations of interest were further visually inspected in tumor andnormal sample sequences through using Integrative Genomics Viewer (IGV),version 2.3.23.

Gene Expression Analyses

Data were obtained using a HumanHT-12 v4 Illumina beadarray technology.Following data normalization, genes were collapsed to the probedisplaying highest mean signal. Gene expression values were then Log2-transformed and centered to the median IRS2 expression in tumorgraftsscored as sensitive or resistant to cetuximab was compared by two-tailedStudent's t-test.

Statistical Analyses for Genes with Somatic Alterations

Using the approach previously described in (6), we analyzed 24,334somatic mutations (nonsynonymous and synonymous single basesubstitutions plus indels) identified in the protein coding sequence of127 tumorgraft samples, after samples with KRAS hotspot mutations(codons 12 or 13) and those with a mutator phenotype were excluded. Weimplemented the following statistical framework to identifysignificantly mutated genes by incorporating background mutation rates,gene length, and base composition.

Inspired by previous works (7, 8), our model defines gene-specificbackground mutation rates, which capture exome-wide as well asgene-specific sequence-based parameters. We define 8 exhaustive anddisjoint sequence-based dinucleotide contexts: C in CpG, G in CpG, C inTpC, G in GpA, and all other A, G, C, T. We represent the occurrences ofeach context in the entire protein coding sequence by N_(i), and in eachgene of interest by g_(i). Subsequently, we identify the dinucleotidecontext for all single base substitution (SBS) somatic mutationsidentified and derive the counts of mutations in each context over allCDS (protein coding sequence) (n_(i)). We derive the expectedprobability of observing a mutation in a base occurring in the CDS of agene of interest as follows:

$\begin{matrix}{P_{mut} = \frac{\sum\limits_{i = 1}^{I}{g_{i}f_{i}}}{\sum\limits_{i = 1}^{I}g_{i}}} & (1) \\{f_{i} = \frac{n_{i}}{N_{i}}} & (2)\end{matrix}$where f_(i) denotes the fraction of bases in dinucleotide context i inthe entire CDS, where a mutation has been observed. The contextparameters N_(i) and g_(i) are defined as the total number ofoccurrences of each context sequenced across all of the samples;therefore following the simplifying assumption of full coverage of theentire protein coding sequence, and assuming K samples total, theseparameters will be K times those of a single haploid exome.

Following the definition of f_(i), we derive the background probabilityof observing at least m_(g,obs) mutations in a gene of interest, usingthe binomial tail probability of L_(g) trials with m_(g,obs) successesand P_(mut) probability of success in each trial. Here, L_(g) representsthe length of the CDS of the gene times the number of samples.

$\begin{matrix}{P_{freq}^{indel} = {{P\left( {m_{g,{mut}} \geq m_{g,{obs}}} \right)} = {\sum\limits_{j = m_{g,{obs}}}^{L_{g}}{\begin{pmatrix}L_{g} \\j\end{pmatrix}{P_{mut}^{j}\left( {1 - P_{mut}} \right)}^{L_{g} - j}}}}} & (3)\end{matrix}$

We use an equivalent formulation to model the statistical significanceof observing q_(g,obs) insertions/deletions (indels) in a gene ofinterest. The background indel frequency (P_(indel)) is defined as thenumber of indels recovered in the entire CDS of the sequenced samplesdivided by the length of the entire CDS available in these samples.

$\begin{matrix}{P_{freq}^{indel} = {{P\left( {q_{g,{indel}} \geq q_{g,{obs}}} \right)} = {\sum\limits_{j = q_{g,{obs}}}^{L_{g}}{\begin{pmatrix}L_{g} \\j\end{pmatrix}{P_{indel}^{j}\left( {1 - P_{indel}} \right)}^{L_{g} - j}}}}} & (4)\end{matrix}$

The two statistical tests described above (3,4) reflect the significanceof mutation counts in a gene, but are blind to the protein-levelconsequence of mutations. To capture the impact of mutation on protein,we apply an extension of the tests above that examines enrichment fornonsynonymous mutations in the set of single base substitution mutationsidentified in a gene of interest. We define a background, gene-specificratio of non-synonymous to synonymous (NS/S) mutations, given theexome-wide NS/S ratio in each dinucleotide context (r_(i)) and thesequence composition of each gene as follows. Note that g_(i) has thesame definition as in (1).

$\begin{matrix}{r_{g} = \frac{\sum\limits_{i = 1}^{I}{r_{i}g_{i}}}{\sum\limits_{i = 1}^{I}g_{i}}} & (5)\end{matrix}$

Given the NS/S ratio for a gene of interest, the probability of anobserved mutation in the gene being nonsynonymous is:

$\begin{matrix}{P_{g,{NS}} = \frac{r_{g}}{r_{g} + 1}} & (6)\end{matrix}$

Following this step, the binomial tail probability of observingm_(g,obs) ^(NP) from the total of m_(g,obs) mutations in a gene ofinterest is:

$\begin{matrix}{P_{composition}^{mut} = {{p\left( {m_{g,{mut}}^{NS} \geq m_{g,{obs}}^{NS}} \right)} = {\sum\limits_{j = m_{g,{obs}}^{NS}}^{m_{g,{obs}}}{\begin{pmatrix}m_{g,{obs}} \\j\end{pmatrix}{P_{g,{NS}}^{j}\left( {1 - P_{g,{NS}}} \right)}^{m_{g,{obs}} - j}}}}} & (7)\end{matrix}$

The three test statistics (3, 4, 7) rely on three distinct measures forcalling a gene significantly mutated: the counts of single basesubstitutions, the counts of indels, and the relative counts ofnon-synonymous to synonymous single base substitutions. Assuming theindependence of these measures, given gene-specific parameters of g_(i)and L_(g), we combine them using Fisher's combined probability test toderive a measure of overall significance for each gene of interest(combined p-value). We acknowledge the fact that Fisher's combinedprobability test is best suited to p-values derived from continuousprobability distribution functions; however, it has been shown that itsapplication to p-values derived from discrete probability distributionsresults in conservative estimates of p-value.

Finally, we apply Bonferroni and Benjamini-Hochberg's correction methodto combined p-values to control for multiple testing.

Statistical Analyses for Therapeutic Resistance or Sensitivity

Statistical models for tumor growth were implemented for each of fourmutation profiles that were correlated to resistance or sensitivity tocetuximab treatment. Group A samples had ERBB2 mutations and/oramplification, MET amplification, EGFR mutations affecting theectodomain or kinase domain, NRAS mutation, BRAF 600V>E, FGFR1amplification, PDGFRA mutations affecting the kinase domain and MAP2K157K>N. Group B samples had ERBB2 mutations, EGFR mutations affecting theectodomain or kinase domain, FGFR1 amplification, PDGFRA mutationsaffecting the kinase domain or MAP2K1 57K>N. Group C samples hadamplification of EGFR or a mutation or amplification of IRS2 while groupD samples had amplification or mutation of IRS2. As IRS2 alterations arelikely to be predictive of anti-EGFR response in cases without othermechanisms of resistance to EGFR therapy, we excluded two samples thatharbored a MET amplification or BRAF mutation from Group C and D. Foreach group, Wilcoxon rank sum and two sample Welch t-tests were used toevaluate differences in the mean tumor growth between samples withmutation and those without. For preclinical models, statisticalcomparisons of treatment efficacy in were performed by two-way ANOVA.

Protein Structure Modeling

The crystal structure of the extracellular domain of the epidermalgrowth factor receptor in complex with the Fab fragment of cetuximab wasretrieved from the protein data bank (PDB entry #1YY9). This PDB entrycontains a complex of 3 biomacromolecules including the extracellularportion of EGFR, cetuximab Fab Light chain, and cetuximab Fab Heavychain. The EGFR-cetuximab complex was visualized using Deep ViewSwiss-pdbviewer (SPDBV_4.10_PC).

References (for Example 6 Only) Incorporated by Reference Here

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We claim:
 1. A method of treating a tumor in a human, comprising: administering afatinib and an anti-EGFR antibody to the human, wherein the human has previously been treated with cetuximab and wherein the tumor is resistant to anti-EGFR antibody blockade, and wherein the tumor comprises a G465R, G465E, or V843I mutation in EGFR.
 2. The method of claim 1 wherein the anti-EGFR antibody is cetuximab.
 3. The method of claim 1 wherein prior to the step of administering, a sample from the tumor is tested and presence of the mutation in EGFR is found in a minority of tumor cells in the sample.
 4. The method of claim 1 wherein the tumor is a colorectal tumor.
 5. The method of claim 1 wherein the anti-EGFR antibody is selected from the group consisting of: Bevacizumab, Cetuximab, Cixutumumab, Dalotuzumab, Figitumumab, Ganitumab, Onartuzumab, and Rilotumumab, and combinations thereof.
 6. The method of claim 1 wherein the anti-EGFR antibody is panitumumab. 